Hyposmolarity stimulates myeloperoxidase exocytosis from human polymorphonuclear leukocytes

Cell swelling-induced peptide hormone secretion

Cell volume changes induced in various ways (anisosmotic environment, hormones, oxidative stress, substrate uptake) are an integral part of a signal transduction network regulating cell function. Cell swelling has received increasing attention as a stimulus for a variety of intracellular phenomena. One of the most remarkable effects of cell swelling is its powerful effect in inducing exocytosis of material in intracellular secretory vesicles. Secretion of essentially all so-packaged hormones including those from hypothalamus (thyrotropin-releasing hormone, TRH; gonadotropin-releasing hormone, GnRH), pituitary (LH, FSH, ACTH, MSH, TSH, prolactin, beta endorphin), pancreas (insulin, somatostatin, glucagon), heart (atrial natriuretic hormone) and kidney (renin) are stimulated in a concentration-related manner by medium hyposmolarity or isosmolar medium containing permeant molecules such as ethanol or urea (reviewed in Ref. 21). Cell swelling-induced exocytosis is not restricted to endocrine cells and hormones; medium hyposmolarity also induces secretion of exocrine pancreatic enzymes and myeloperoxidase from human polymorphonuclear leukocytes.

Cell swelling induced secretion of TRH by posterior pituitary, hypothalamic paraventricular nucleus and pancreatic islets: effect of L-canavanine

The aims of this study were to test if ethanol induces thyrotropin-releasing hormone (TRH) secretion in vitro from the posterior pituitary and hypothalamic explants by a mechanism involving cell swelling, and to characterize the pathway of stimulated secretion. Ethanol, at a concentration of 80 mM, stimulated the release of TRH from the posterior pituitary, the hypothalamic paraventricular nucleus, the median eminence, and the brain septum, when administered only in isosmolar but not in hyperosmolar medium. This indicates the involvement of a cell swelling-inducing mechanism. L-canavanine in a concentration of 3 mM, increased the basal and hyposmosis-induced TRH secretion from the posterior pituitary and the paraventricular nucleus, and both basal and ethanol-induced TRH secretion from isolated pancreatic islets. This indicates the presence of both constitutive and regulatory secretory pathways. Our results suggest that cell swelling induces exocytosis from clathrin coated granules.

Hypotonicity induces L-selectin shedding in human neutrophils

Expression levels of adhesion molecules on neutrophils are affected under various conditions, including ischemia, possibly because of associated increases in cell volume. We examined the effects of cell swelling in hypotonic media on the level of L-selectin (CD62L) and beta(2)-integrin (CD18) on human neutrophils. In hypotonic media, neutrophils shed L-selectin. The shedding was greatly reduced by 30 microM RO31-9790, the metalloprotease (sheddase) inhibitor. Hypotonicity-induced L-selectin shedding was also time and tonicity dependent. Decreasing tonicity caused increased shedding. In 0.6x medium (0.6x the normal tonicity of 300 mosmol/kgH(2)O), shedding increased over a 2-h period, after which >70% of the neutrophils had lost L-selectin. In contrast to L-selectin, the level of beta(2)-integrin on the neutrophil surface was not significantly affected. Thus L-selectin shedding, which occurs on neutrophil activation and is usually accompanied by beta(2)-integrin upregulation, was selectively induced by hypotonicity without a corresponding effect on beta(2)-integrin.

Hyperosmolarity-induced gene stimulation is mediated by the negative calcium responsive element

The negative calcium responsive elements of the parathyroid hormone gene bind to a specific set of nuclear proteins in an extracellular calcium (Ca2+e)-dependent manner. We have found that one of the negative calcium responsive elements, named oligo B, is found in the 5'-flanking region of such vasoactive genes as the vasopressin and atrial natriuretic polypeptide genes. Furthermore, the oligo B-like sequence in the former gene is conserved throughout evolution. Because expression of some of these vasoactive genes is altered by external stimuli which change cell volume, we examined whether oligo B is involved in gene regulation by hyperosmolarity. Here, we demonstrate that the binding between oligo B and its binding nuclear proteins including a redox factor 1 was reduced by hyperosmolarity generated by sodium chloride but not by urea. Such attenuated binding was reversed by dephosphorylating nuclear proteins by a potato acid phosphatase, suggesting that NaCl treatment elicited phosphorylation of these nuclear proteins to weaken their binding activity to oligo B. Furthermore, these nuclear events led to hyperosmolarity-mediated transcriptional stimulation of the genes bearing this DNA element in the cultured cells.

Both iso- and hyperosmotic ethanol stimulate release of hypothalamic thyrotropin-releasing hormone despite opposite effect on neuron volume

Previous studies have indicated that isosmolar, but not hyperosmolar, ethanol induces in vitro gonadotropin-releasing hormone secretion from the basal hypothalamus, presumably by causing cell swelling. Moreover, ethanol reduces secretion of another hypothalamic neuropeptide vasopressin. We have studied the acute effect of ethanol on specific hypophysiotropic basal and K+-stimulated thyrotropin-releasing hormone secretion in vitro especially in relation to cell swelling. Isosmotic 40-160 mM ethanol increased thyrotropin-releasing hormone release from the hypothalamic paraventricular nucleus and median eminence in a dose-dependent manner. Both a 30% decrease of osmolarity and isosmotic 80 mM ethanol induced 12% swelling of hypothalamic neurons. Hyperosmotic 80 mM or 160 mM ethanol induced release of thyrotropin-releasing hormone from both hypothalamic structures but did not cause cell swelling (80 mM) or even induced cell shrinkage (160 mM). Depletion of medium Ca2+ did not affect thyrotropin-releasing hormone secretion caused by either isosmotic or hyperosmotic ethanol. Our data indicate that both iso- and hyperosmotic ethanol stimulated release of hypophysiotropic thyrotropin-releasing hormone despite opposite effects on neuron volume. The mechanism of ethanol action appears complex and variable depending on the type of cell and neuropeptide affected.

50-mile walking race suppresses neutrophil bactericidal function by inducing increases in cortisol and ketone bodies

To examine the effect of intensive aerobic exercise on the interaction between endocrine and immune systems, we studied in ten normal healthy male subjects the effect of a 50-mile walking race on blood concentration of hormones (insulin, GH, ACTH, cortisol, adrenaline, noradrenaline, and dopamine), ketone bodies, specific immunological functions (IgG, IgM, and PHA/Con A-induced lymphocyte blastformation test), and nonspecific immune (CH50, and neutrophil bactericidal functions). Neutrophil bactericidal activity was measured as chemiluminescences amplified by luciferin analog (CLA-DCL) and luminol (L-DCL). The race increased cortisol and ketone bodies, and decreased insulin, CLA-DCL, and L-DCL (all parameters; P < 0.01). However, other parameters were not significantly changed. There were significant negative correlations between changes of ketone bodies/cortisol and CLA/L-DCL (P < 0.05), however there was no significant correlations between changes of insulin and CLA/L-DCL. These data indicate that extensive aerobic exercise causes impaired neutrophil bactericidal function, probably due to the induced increases in both cortisol and ketone bodies. This impaired neutrophil function may cause the susceptibility to infection after an extensive exercise.

Hypertonic glucose inhibits the production of oxygen-derived free radicals by rat neutrophils

We studied the influence of graded degrees of hypertonic glucose or sucrose on the generation of oxygen-derived free radicals by rat neutrophils. Hypertonic glucose and sucrose exerted dose- and time-dependent inhibition of chemiluminescence amplified by luciferin analog (CLA-DCL) and luminol (L-DCL) in response to fMLP. Hypertonic glucose was more effective to this chemiluminescence inhibition than hypertonic sucrose was. This inhibition of hypertonicity was more effective in CLA-DCL than in L-DCL. Although the production of superoxide anion measured by the reduction of ferricytochrome c was more inhibited by hypertonic glucose than by hypertonic sucrose, the myeloperoxidase activity was not affected by either glucose or sucrose hyperosmolarity. These data suggest that hyperosmotic state by itself and an additional direct glucose-toxicity may contribute to the impaired neutrophil function in the diabetic state.

Cell swelling induced by medium hyposmolarity or isosmolar urea stimulates gonadotropin-releasing hormone secretion from perifused rat median eminence

Medium hyposmolarity between 10 and 50% and isotonic urea between 22.5 and 90 mM induced a dose-dependent burst of gonadotropin-releasing hormone (GnRH) secretion from perifused median eminence tissue which was maximal at 2-3 min and returned to near baseline by 5 min in spite of continued exposure to the stimulus. If Ca(2+)-free medium was used, osmotic stimulation of secretion was increased or unchanged, but secretion induced by 30 mM K+ was markedly reduced. Our data indicate that cell swelling induced by medium hyposmolarity or permeant molecules stimulates GnRH secretion from median eminence cells or cell processes as it does secretion from normal endocrine cells containing hormone stored in intracellular vesicles. In both, Ca2+ influx is not required or has a negative modulating influence on cell swelling-induced secretion.

Lidocaine inhibits prolactin secretion in GH4C1 cells by blocking calcium influx

The mechanism of the inhibitory effect of local anesthetics on hormone secretion was studied in the GH4C1 line of rat pituitary tumor-derived cells. Lidocaine between 0.1 and 5 mM exerted significant dose-dependent inhibition on the increment in cytosol Ca2+ concentration ([Ca2+]i) and prolactin (PRL) secretion induced by 30 mM K+. For both effects the IC50 was 0.25 mM and maximal inhibition occurred at 5 mM. A normal response returned within 20 min after removal of lidocaine from the incubation medium. 1 microM tetrodotoxin had no effect on the 30 mM K+ induced [Ca2+]i transient or PRL secretion, indicating that Na+ channels are not involved in the inhibitory effect of lidocaine. Lidocaine similarly inhibited the [Ca2+]i increment and PRL secretion induced by 30% medium hyposmolarity and 1 microM Bay K 8644. Lidocaine was much less effective in inhibiting secretion induced by 1 microM phorbol 12-myristate 13-acetate (TPA) or 5 microM forskolin. 5 mM procaine produced effects similar to those of lidocaine. Our data suggest that in GH4C1 cells local anesthetics depress secretagogue-induced PRL secretion primarily by blocking Ca2+ influx, probably through L-type Ca2+ channels.

Mechanism of inhibitory action of ketone bodies on the production of reactive oxygen intermediates (ROIS) by polymorphonuclear leukocytes

We determined an effect of acetoacetic acid (AcAc) and 3-hydroxybutyrate (3-OHB) on the production of reactive oxygen intermediates (ROIs) in polymorphonuclear leukocytes from healthy volunteers. Both AcAc and 3-OHB inhibited the luminol-dependent chemiluminescence (LDCL) activities assessed with initial slope and the inhibition rates were about 42%, 44% respectively by AcAc and 3-OHB when the leukocytes were preincubated with 10 mM AcAc or 3-OHB for 60 minutes. The LDCL activity was reduced by 16% and 42% following the addition of 1mM and 10 mM AcAc. The similar reduction of the LDCL activity was observed in the addition of 3-OHB. Either 3-OHB or AcAc failed to show a significant reduction of myeloperoxidase (MPO) activity. However, both 3-OHB and AcAc dose-dependently inhibited superoxide anion (O2-) production, measured by using cytochrome c. These data provided evidence that both 3-OHB and AcAc suppress neutrophil oxidative metabolism with respect with O2- production.

Medium hyperosmolarity depresses thyrotropin-releasing hormone-induced Ca2+ influx and prolactin secretion in GH4C1 cells

We studied the influence of graded degrees of hyperosmolarity on the dynamics of the thyrotropin-releasing hormone (TRH)-induced rise in cytosol Ca2+ concentration ([Ca2+]i) and prolactin (PRL) secretion in GH4C1 cells. TRH caused two phases of increase in [Ca2+]i that were differentially altered by hyperosmolarity: 100% hyperosmolarity (600 mOsm) depressed only 20% of an initial high-amplitude [Ca2+]i burst (first phase) dependent on Ca2+ mobilized from intracellular pools, but it abolished a sustained low-amplitude second phase dependent on extracellular Ca2+ influx. Low degrees of hyperosmolarity suppressed PRL secretion due to Ca2+ influx while high degrees suppressed secretion due to mobilized Ca2+. These data suggest that in GH4C1 cells hypertonic inhibition of secretion may result from both blocking Ca2+ influx and mechanisms unrelated to [Ca2+]i.